The debate over the appropriate use of high cost technologies, typified by radiologic procedures, is in part the consequence of methodologic difficulties in the assessment of these procedures. Such assessment is subject to several sources of bias which limit the reliability of results and make it difficult to generalize them to clinical settings other than the one in which the assessment was carried out. The aims of this proposal are to develop statistical methodology for correcting two specific biases, verification bias and referral bias, to empirically evaluate the methodology as applied to specific radiologic procedures used in cancer detection and diagnosis, and to make recommendations for future experimental design which will expedite assessment of and correction for such biases. The researech is collaborative, involving both statisticians and a radiologist, and consequently will span both disciplines. We believe that the research has important implications to the field of diagnostic test evaluation,